They are primarily designed to kill flies. While I haven't had much use for it yet, because I received mine around Thanksgiving, so the fly problem is subdued by the cooler temps, I have had success with it.
As for wasps, I used it one time to take one out. It didn't kill it, but stunned it, sent it to the ground and I ended it with my foot. A buddy has 2 also, and has taken out a couple of cockroaches with 2 shots each. The bigger insects require a little closer range than the effective 3' range for the common fly.
Best thing is that like the video shows, it doesn't splatter the insect and is only using table salt as the ammo, so when I've been outside smoking or grilling, I'm not too worried about food contamination and at the very worst, just adding an extra pinch of salt to the vittles.